In order to reduce the vibration and noise of gear in the process of power transmission and reduce the impact in the process of gear meshing, gear modification must be carried out. Gear modification can be divided into two types: profile modification and tooth direction modification.

Due to the manufacturing error and the influence of load, gear will have a certain amount of deformation, such as bending deformation, torsion deformation, shear deformation, etc. These deformation will cause one end of the gear eccentric load and affect the transmission performance of the gear. Tooth direction modification is to modify the tooth direction according to the deformation of the gear, so as to improve the load distribution of the gear teeth. The commonly used method of tooth profile modification is tooth profile modification. As shown in figure a, it is the tooth profile after drum modification. As shown in Figure B, it is the schematic diagram of tooth profile modification. It can make up for the assembly error and the deformation caused by the force effectively by using the tooth direction drum.

Tooth drum shape is a very important design parameter in tooth drum repair, which has a great influence on the bearing capacity of gear. The calculation formula of drum shape given by ISO standard is as follows:

Where f β x is the equivalent skewness.